Analysis of forces developed during mechanical preparation of extracted teeth using Profile NiTi rotary instruments

Aim The aim of this study was to analyse the vertical forces and torque dev eloped in the root canal system of extracted teeth during mechanical prepar ation using ProFile NiTi instruments. Methodology Instrument wear and fracture is in great part due to the repeat ed application of forces and torque during the course of root-canal prepara tion but research into the direct relationship has been hampered by the lac k of adequate measuring devices, Measurements of these forces and torque we re made with a new force analyser device, the Endographe, that was equipped with a holder to record and generate graphs of the vertical forces and tor que exerted during the preparations, These preparations were performed by e ndodontists or students either with a series of instruments of increasing s ize or with the crown-down pressureless technique. Results The mean values for the endodontists of the generated vertical forc es and torque varied, respectively, from 4 to 6N and from 7.105 to 12.105 N m for the step-back technique and from 2.9 to 4.2 N and from 18.105 to 20.1 05 Nm for the crown-down technique. This suggested that the crown-down tech nique generated lower stresses (lower torque and lower vertical forces), al though these findings also depend on the shape of individual canals, The st udents initially showed wide variations in generated forces, with significa ntly lower vertical forte and torque values. By the end of the experimental sessions their values were similar to those of the endodontists, which ind icated improvement in the efficiency of manipulation. Conclusions Further work. is needed to investigate the relationship between the force and the torque data from this study and the incidence of instrum ent fracture with the two techniques, as the clinical implications are cons iderable. It must be noted, however, that the Endographe is unable to take into account the cutting efficiency of the instruments. The use of graphs p rovides a new approach to the analysis of mechanical preparation.